Catheters comprise tube-like members that are inserted into the body for various medical reasons, some diagnostic and others therapeutic. While in many instances the steerability or directionality of such catheters is of concern, steerability is particularly important with regard to certain urological or cardiovascular applications.
There have been various attempts to develop steerable catheters. For example, U.S. Pat. No. 1,060,665 describes an early attempt to provide a catheter capable of some direction. However, the device disclosed in this patent, as well as catheters and catheter guides disclosed in later patents, such as U.S. Pat. Nos. 2,574,840 and 2,688,329, tend to be characterized by only limited directionality.
In addition, some supposedly steerable catheters are too large and rigid to be of practical use in cardiovascular techniques. See, for example, U.S. Pat. Nos. 3,470 876 and 3,605,725, where wires equidistantly positioned along the length of a catheter are connected to a steering means which pulls on the wires to cause the distal end of the catheter to go in a desired direction. Moreover, U.S. Pat. Nos. 3,521,620, 3,547,103, 3,625,200, and 4,020,829 describe coil spring guide wires that have a certain degree of directionality but are too rigid for safe usage in certain delicate cardiovascular procedures.
According to U.S. Pat. No. 4,033,331, a coronary catheter has a main lumen and a shaping wire lumen. When the wire is withdrawn through the shaping wire lumen, the catheter assumes certain predetermined configurations. While this so-called steerable catheter is useful in some cardiovascular applications, such as positioning the initial guiding catheter guide through which other devices are guided, its limited directionality and limited tip control preclude extensive use.
A medical procedure known as percutaneous transluminal coronary angioplasty (PTCA) was developed in approximately 1976-1977 by Dr. Andreas Gruntzig According to this procedure, blockage in a coronary artery can be reduced by positioning a balloon dilatation catheter across the blockage and inflating the balloon, which causes the blockage to decrease. Such positioning requires that the balloon dilatation catheter be "steered" into place, that is, across the stenotic lesion causing the blockage, by manipulation at the proximal end of the catheter
The procedure is actually somewhat complex, consisting of introducing a catheter system via the femoral or brachial artery under local anesthesia. A pre-shaped guiding catheter is positioned into the orifice of the coronary artery, and through this guiding catheter a second dilatation catheter is advanced into the branches of the coronary artery. The dilatation catheter has an elliptically shaped balloon portion near the tip which can be inflated and deflated After traversal of the stenotic lesion of the coronary artery, the balloon portion is inflated with fluid, which dilates the lumen of the vessel.
The PTCA procedure and equipment have become increasingly refined over the past six years. The first marketable PTCA apparatus consisted of a small catheter with a single balloon port and no central lumen, that is, a so-called "fixed wire" system, which terminated in lateral openings at the distal end thereof This system, which is the subject of U.S. Pat. No. 4,195,637, was designed by Dr. Gruntzig and was marketed in the U.S. by USCI. The fixed wire catheter system disclosed in U.S. Pat. No. 4,195,637 comprises a balloon dilatation catheter and a low friction guide catheter consisting of one tubular member fitted into a more rigid, shrunk-on tubular member that is not co-extensive the distal end of the balloon dilatation catheter has a flexible tip advantageously fabricated from a spring steel wire.
In 1980-1981 Dr. John Simpson, working at Stanford University, began to modify the fixed wire system and eventually developed a catheter with a free central lumen for movable guide wires. This catheter system is the subject of U.S. Pat. No. 4,323,071, which is assigned to Advanced Cardiovascular Systems, Inc. (ACS), formerly known as Advanced Catheter Systems, Inc. By use of such a movable wire system, one could more readily select the desired coronary artery and reach smaller branches since the movable guidewires are inherently smaller and more flexible than the fixed wire system. Movable guidewires are particularly useful in a technique known as catheter exchange, whereby one catheter positioned concentrically around a guidewire is replaced by, i.e., exchanged for, another such catheter, the guidewire maintaining the desired position. Subsequent to the development of the catheter with movable guidewires, known as the Simpson-Robert system and marketed by ACS, USCI has abandoned the fixed wire system and has marketed a similar device, calling it the steerable catheter, DILACA.RTM..
Samson, U.S. Pat. No. 4,516,972 issued May 14, 1985, to ACS. This patent: is directed to a guide catheter having a helically wound ribbon of flexible material imbedded in the wall of the catheter to provide torsional rigidity.
There is a further catheter system in use known as the Hartzler low profile catheter system. According to this catheter system a balloon dilatation catheter has a concentrically contained guidewire extending the length of said catheter. Moreover, the distal end of the guidewire extends a short distance beyond the distal end of the balloon dilatation catheter and is affixed to the distal end of the balloon dilatation catheter.
The catheter system with movable guidewires and the low profile catheter system each represent an advance but still have disadvantages such as limited steerability, which is at present dependent upon the torquability, or torque control, of the movable wire. Steerability is highly significant in a cardiovascular procedure such as PTCA, or angioplasty, because less steerability results in greater time spent in the body and more possible patient trauma. Multiple insertions of guidewires and catheters can lead to thrombosis in that coagulation may commence along a guidewire surface and be forced into the heart when a catheter is slid over the guidewire. Furthermore, there are some blockages which simply cannot be reached with presently known equipment.
Co-pending U.S. patent application Ser. No. 193,201 filed May 9, 1988, and U.S. patent application Ser. No. 213,662, filed June 30,1988, and U.S. Pat. No. 4,723,936, all of which are incorporated herein by reference, are directed to improved steerable catheter means useful in, for example, cardiovascular applications. The catheter means disclosed therein are characterized by a relatively low profile and enhanced directionality due to combined rotation of the catheter means and active deflection of the catheter tip.
As mentioned above, PTCA technology appears to be directed toward fixed wire dilatation catheters, especially low profile catheters To achieve such low profiles, it has been necessary to abandon the through lumen of the movable guidewire catheter, a design change which has precluded standard exchange techniques wherein dilatation balloons are changed over a guidewire. In addition, a guidewire cannot be maintained in position across and past a stenosis once dilatation is complete because as soon as a fixed wire catheter is withdrawn, the position across and beyond the stenosis is lost.